PROJECT SUMMARY/ABSTRACT Development of effective therapies is an urgent, unmet medical need for patients with pancreatic ductal adenocarcinoma (PDAC). The advent of immune checkpoint antagonists such as anti-PD-1 and anti-CTLA4 antibodies has revolutionized treatment of some cancers but remains unsuccessful in PDAC. We and others showed that the tumor microenvironment (TME) of PDAC is rife with myeloid-derived suppressor cells including inflammatory monocytes (IMs) and tumor-associated macrophages (TAMs) that stifle the effect of chemotherapy and anti-tumor immunity. Excessive production of CCL2 in PDAC has shown to result in tumor growth, dissemination, local immunosuppression, and resistance to chemotherapy. Targeting a key chemotactic mechanism, the C-C motif chemokine ligand 2 (CCL2)/ C-C chemokine receptor type 2 (CCR2) axis, that draws these cells to the TME potentiates the efficacy of chemotherapy in preclinical mouse model and a clinical trial conducted at our institution, setting the premise to further confirm and optimize CCR2-targeted strategies in PDAC. We are in the process of opening a phase I/II clinical trial combining a CCR2/5 inhibitor, chemotherapy and anti-PD-1 agent. Realizing that not all patients will benefit from this regimen, a diagnostic tool capable of assessing CCR2 abundance while predicting and monitoring treatment response will be invaluable. CCR2 inhibitor slows tumor progression, prevents metastasis in mouse models of PDAC, and potentiates effect in patients with border-line resectable or locally-advanced PDAC (NCT01413022). We have developed a CCR2- PET tracer (64Cu-DOTA-ECL1i) and shown its sensitivity and specificity in imaging CCR2 in multiple preclinical inflammatory disease models and PDAC models and PDAC human specimens. Our PDAC PET imaging in genetic mouse model demonstrated early, sensitive, and specific detection of CCR2 in tumors. The first- in-man imaging showed low accumulation of 64Cu-DOTA-ECL1i in normal pancreas and liver (a common site of metastatic disease where CCR2-bearing IMs and TAMs infiltrate the pre-metastatic sites prior to establishment of metastatic clones) with rapid blood and renal clearance, indicating the potential of this PET tracer for CCR2 detection in PDAC patients. We hypothesize that 64Cu-DOTA-ECL1i can sensitively and specifically detect CCR2 in PDAC, track the variation following CCR2-targeted treatment, and likely prescreen PDAC patients for CCR2-targeted therapy. We propose to evaluate whether tumor uptake of 64Cu-DOTA-ECL1i correlates with tumor expression of CCR2 and response to standard chemotherapy in PDAC patients. We also will evaluate whether tumor uptake of 64Cu-DOTA-ECL1i predicts response to CCR2-directed therapy in PDAC patients treated with CCR2/5 inhibitor and chemo-immunotherapy. The successful completion of this grant will facilitate innovative means for clinical data interpretation, patient stratification, and therapy guidance.